1. Field of the Invention
This invention relates to clear, aqueous liquid preparations of sodium salts of linear alkylsulfates which, by virtue of their composition and performance properties, are particularly suitable for use as surfactant components in the manufacture of toothpastes.
2. Discussion of Related Art
Dilute aqueous solutions of sodium-n-alkylsulfates containing from 12 to 16 carbon atoms show a tendency towards clouding and precipitation of undissolved alkylsulfate, even at temperatures above 10.degree. C. The reason for this is the relatively poor solubility of these alkylsulfates in water at temperatures below the critical solution temperature or rather the Krafft temperature, i.e., the temperature above which there is a sudden increase in water solubility through increased micelle formation. In the case of sodium dodecylsulfate, for example, this temperature is at 8.degree. C. and, for sodium tetradecylsulfate, is at 20.5.degree. C. (cf. H. Lange and M. J. Schwuger, KolloidZeitschrift and Zeitschrift fur Polymere, Vol. 223 (1967), pages 145 to 149).
Sodium-n-alkylsulfates are suitable for numerous commercial applications by virtue of their favorable foaming properties and their cleaning effect. Their neutral flavor, their acceptable compatibility with mucous membrane, and their growth-inhibition effect on the bacteria responsible for plaque make them particularly suitable for use as a surfactant component in the production of oral hygiene and dental care preparations. The products are typicaly used as spray-dried or recrystallized, fine crystalline powders for these applications. This gives rise to the disadvantage of considerable dust emission in use and the unwanted entry of air into the product.
The use of the products in dissolved form is prevented by their limited solubility in water. It has previously been proposed to mix the sodium-n-alkylsulfates with water and glycerol and/or sorbitol, however, the suspension obtained has to be subjected to prolonged degassing at elevated temperature before it can be used in the production of toothpastes.
Accordingly, there is a need for an aqueous preparation of sodium-n-alkylsulfates in the form of a clear solution having a low cloud point which is suitable for the practical application of the sodium-n-alkylsulfates, particularly for the production of toothpastes and mouth lotions, without any of the disadvantages mentioned above